Flux



Patented June 22, 1943 1 @FFEQE FLUX John D. Coleman and Charles W. Ewing, Dayton, Ohio, assignors to General Motors Corporation, Dayton, Ohio, a corporation of Delaware No Drawing. Application June 17, 1940, Serial No. 340,996

l Claims.

This invention relates to chemistry and more particularly to fluxes.

It is an object of our invention to provide a series of fluxes for wide general use which may have their composition varied to obtain desired melting and pouring points for any particular fluxing application.

It is another object of our invention to provide a flux for hard soldering which has good wetting and free flowing properties as well as excellent cleaning properties and which has no diflicult residue problem.

It is a more specific object of our invention to provide a flux for hard soldering, especially for low melting silver solder, which will have general application and which has excellent fluxing properties and can be made at a reasonable cost.

As one specific example of our invention we provide a flux formed of the following materials:

Anhydrous boric acid 129 lbs. 44% by weight Anhydrous potassium fluoride 9'7 lbs. 33% by weight 52% hydrogen fluoride, 32 lbs. 10.9% by weight Water 35 lbs. 12.1% by weight Igepal C 50 cc.

The process of making this flux is very critical with respect to percentages of ingredients and temperature control. The agitator and the drum used in this process should be clean and dry. The cooling water used in cooling the agitator should be turned off at the start of the process. The first step is to carefully weigh the potassium fluoride and pour it into the drum. The second step is to weigh the water and to pour all the water into the drum. The agitator should be started immediately after the water is added. While the potassium fluoride is dissolving the boric acid may be weighed.

Before adding any of the boric acid, however, 50 cc. of Igepal C (that is a product having the general formula in which n is 6 or more and a: is 3 or more) or some other suitable wetting agent should be added. 1

The use of a wetting agent such as Igepal C is not necessary but it is useful for assisting in the solution of the boric acid by its wetting action. In addition some advantage is gained in the application of the flux to cold working surfaces which are somewhat greasy by nature, since it enables an unbroken film of flux to be formed on such surfaces by the action of the wetting agent. The proportion of such a wetting agent in the flux is insufiicient to produce any appreciable charred residues. Where the surfaces are properly preheated, the presence of a wetting agent is not required to provide proper wetting since the alkalinity of the flux is sufficient to cut or dissolve any greasy film and thereby properly wet the surfaces.

After the potassium fluoride is dissolved, the anhydrous boric acid should be added slowly. The boric acid should be added slowly enough that a thick layer does not float on top of the solution. After all the boric acid has been added the agitator should be allowed to continue operation. After this the hydrofluoric acid should be weighed and connected to the syphon.

For safety the remainder of the process must take place beneath a ventilating hood with the ventilatin fan in operation. When all or substantially all of the boric acid has been dissolved, the hydrofluoric acid should be allowed to flow slowly into the drum. At the time the acid starts flowing, the temperature will be about F. The temperature will rise rapidly and when the temperature reaches F. the cooling water valve should be opened and the flow of cooling water should be adjusted so that the temperature ranges between 120 F. and F. while the remainder of the hydrofluoric acid flows into the drum.

The stirring of the mixture should be continued and then the flow of cooling water should be increased to allow the temperature to drop rapidly until 100 F. is reached. As soon as 100 F. is reached the cooling water should be shut off, but stirring of the mixture should be continued. The flux is then ready to be drawn into containers and should be passed through a fairly coarse screen to remove impurities as it goesfrom the drum. The flux should be poured directly into the proper containers immediately and the lids screwed on. The containers should be allowed to remain undisturbed until the flux has dropped to room temperature and has taken itsv normal set after which it can be handled.

Precautions to be observed .added, or caking and hardening will occur.

4. Do not allow temperature to rise above 125 F. while the hydrofluoric acid is being added or below 120 F. after that temperature is reached. Temperatures of above 125 F. cause the flux to grow into large grainy crystals. Allowing the temperature to fall below 120 F. after it has reached that temperature may cause the flux to thicken so much that it cannot be stirred.

5. If the hydrofluoric acid stops flowing for any reason before it is all gone, shut the cooling water ofl immediately to prevent the temperature falling below 120 F.

6. After all the hydrofluoric has all been added, do not cool the flux below 100 F. or you are very apt to cause it to thicken so much that it will not flow out of the drum.

7. The operator should not leave the machine after the hydrofluoric is started in until the batch is bottled.

The resultin product is alkaline in character and appears to be a complex potassium fluoroborate having an excess of boric acid over and above the quantity required to make normal potassium fiuoroborate. This product is stable at soldering and brazing temperatures and melts at about 700 F. and has a pouring point of about 750 F. It flows freely and cleans metal well, and makes possible better soldering and brazing than was produced by ,fluxes previously used. A particular advantage of this flux is that it has a definite reducing property at soldering and brazing temperatures. Metal salts are reduced by the action of the flux and the use of this flux makes it possible to coat metals by this reducing action upon any metal salts present. This has been taken advantage of in the fluxes intended for use in hard soldering brass by adding about 2% of copper acetate to the flux. This addition of copper acetate raises the melting point slightly, but provides very superior wettin properties on brass. However; it is not advisable to use the copper acetate when the flux is used in connection with ferrous materials.

The melting point of the flux may be lowered by increasing the proportion of hydrofluoric acid so that the melting point may be reduced to about 500" or 600 F. The melting point may be raised to as much as 1000 F. by lowering the proportion of hydrofluoric acid.

It is not necessary to make this flux to use the specific materials set forth above. For example, instead of boric acid some borate may be used, such as potassium borate, which may be mixed in the initial step with hydrofluoric acid to provide the same result as is obtained with boric acid and potassium fluoride. Likewise sodium borate might be used in the initial step with hydrofluoric acid in order to obtain a product containing sodium.

It is not necessary that potassium fluoride be used, or to depend on potassium for the metallic radical in the first step. but sodium, lithium, calcium, magnesium or strontium fluoride, having similar properties, may be used instead of the potassum fluoride. Of this group, potassium, lithium and sodium appear to be superior for most purposes. However, the use of these other materials changes the melting point and therefore, by the use of these materials the temperature range of this series of fluxes is greatly extended. For example, the use of sodium fluoride provides a soldering flux which by varyin the amounts of the hydrofluoric acid will have a melting point range of from about 1000 F. to

used for fluxing molten iron and steel and for some welding applications.

It is not necessary to use hydrofluoric acid, but any source of hydrogen fluoride which leaves no residue may be used. For example, the dry hydrogen fluoride gas or some relatively unstable fluoride such as ammonium bi-fluoride or some amine fluoride may be used instead. When ammonium bi-fluoride is used a much slower reaction takes place when it is introduced during the second step of the process. If desired, other grades of hydrofluoric acid may be used with corresponding adjustments in the formulae.

By making appropriate changes in the initial step, an alkali fluoride or alkali hydroxide such as potassium, sodium, lithium or calcium carbonate or hydroxide may be used and hydrofluoric acid added to form the alkali fluoride prior to the addition of the boric acid.

In order to obtain the best flux for hard soldering the proportion of potassium fluoride to boric acid should be maintained at about the proportions set forth above. Instead of anhydrous potassium fluoride, other forms of potassium fluoride may be used. This reduces or sometimes eliminates the requirement for the addition of water.

Preferably the formulae for the different types of fluxes should be limited as follows:

Anhydrous basis Boric acid 30% to60% Alkali fluoride 20% to Hydrogen fluoride 2% to 10% Water, quantity suflicient to make Boric acid 40% to80% Alkali carbonate", 10% to 50% Hydrogen fluoride 2% to20% Water, quantity suflicient to make 100% Boric acid 40% to 80% Alkali hydroxide 10% to50% Hydrogen fluoride Water, quantity suflicient to make 100% While the form of embodiment of the invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. A flux comprising a product formed by first mixing boric acid and a normal fluoride of a metal selected from the group consisting of lithium, sodium, potassium, magnesium, strontium, and calcium and then mixing the resultant product with a material which will yield hydrogen fluoride without leaving a solid residue.

2. A flux comprising a product formed by first mixing boric acid and a normal fluoride of a metal selected from the group consisting of lithium, sodium, potassium, magnesium, strontium, and calcium and then mixing the resultant product with hydrogen fluoride.

3. A flux comprising a product formed from the following materials including a material selected from a group consisting of lithium, sodium, potassium, magnesium, strontium, and calcium normal fluoride, boric acid, and a material which will yield hydrogen fluoride without leaving a solid residue, the molecular ratio of the hydrogen fluoride content to the normal fluoride content and to the boric acid content being each about in the ratio of 1 to 2.

4. A flux comprising a product substantially entirely formed from the following materials including a material selected from a group consisting of lithium, sodium, potassium, magnesium, strontium, and calcium normal fluoride, boric acid, water and hydrogen fluoride, the molecular ratio of the hydrogen fluoride content to the normal fluoride content and to the boric acid content being each about in the ratio of 1 to 2.

5. A flux comprising a product formed by flrst reacting boric acid with a material selected from tent as well as to the boric acid content are each I about in the ratio of 1 m2.

7. A flux formed of materials providing hydrogen fluoride, normal alkali fluoride, and boric acid radicals in which the molecular ratio of the hydrogen fluoride content to the normal alkali fluoride content is about in a ratio of 1 to 2 and the molecular ratio of the hydrogen fluoride content to the boric acid content is between about 1 to 2 and 1 to 3 on an anhydrous basis.

8. A flux comprising a product formed by flrst mixing boric acid and a normal fluoride of a metal selected from the group consisting of lithium, sodium, potassium, magnesium, strontium, and calcium and then mixing the resultant product with a material which will yield hydrogen fluoride without leaving a solid residue in which the molecular ratio of the hydrogen fluoride content to the normal fluoride content is about in the ratio of 1 to 2 and the molecular ratio of the hydrogen fluoride content and the boric acid content is between about 1 to 2 and 1 to 3 on an anhydrous basis.

9. A flux comprising a product formed by first mixing boric acid and normal potassium fluoride, and then mixing the resultant product with hydrogen fluoride, the molecular ratio of the hydrogen fluoride content to the normal potassium fluoride content being about in a ratio of 1. to 2 and the molecular ratio of the hydrogen fluoride content to the boric acid content being between about 1 to 2 and 1 to 3, all on an anhydrous basis.

' 10. A flux comprising a product formed of boric acid, normal potassium fluoride, and hydrogen fluoride in which the molecular ratio of the hydrogen fluoride content to the normal p0- tassium fluoride content is about in the ratio of 1 to 2 and the molecular ratio of the hydrogen fluoride content to the boric acid content is between about 1 to 2 and 1 to 3, all on an anhydrous basis.

JOHN D. COLEMAN.

CHARLES W. EWING. 

